Moving Picture Experts Group (MPEG), a series of international standards for moving picture compression established by the moving picture experts group, has been widely applied in the fields like digital television, CD, DVD, video on demand, etc. It is defined in MPEG a TS that can be remotely transmitted in a noisy channel. The so-called TS is a single data stream, which is formed by one or a plurality of program elementary streams having a common time base or independent time bases and bears MPEG data streams to be transmitted.
At present, there are mainly two kinds of standard baseband transmission interfaces for TS transmission: one is Synchronous Parallel Interfaces (SPI) and the other is Synchronous Serial Interfaces (SSI). For convenience in the TS transmission, the existing MEPG decoding and encoding chips are all fitted with standard SPI and/or SSI.
To ensure normal profits of the cable television value-added services in a digital television application, provided in the prior art is Conditional Access (CA). This CA is a technical means, which can be implemented by a Conditional Access System (CAS) for the purpose that only authorized user terminals are allowed to watch a corresponding TS and unauthorized user terminals are unable to receive the TS. To achieve this purpose, CA encryption needs to be performed on the TS before the TS is sent to the user terminals, and when the CA-encrypted TS reaches the user terminals, CA descrambling is performed on the TS using a decryption key that is notified during authorization, after that, video decoding is performed and the resulting video is eventually offered to the users.
At present, the solution of CA descrambling is mainly a CA on-chip integration solution, i.e. CA descrambling and video decoding are set in the same main chip, this is one of the main forms of the current set-top boxes. In this solution, the scrambled TS is no longer output in a transparent form after entering the main chip, thus ensuring the security of the TS. This solution, however, is incompatible with different operators. For example, a main chip that can work normally in Beijing fails to do that in Shanghai owing to different operators.
To solve the problems above, further provided in the prior art are two solutions below:
One of these two solutions is a CA separation solution, which mainly comprises: an encrypted TS is transmitted, via an interface, to a dedicated CA card with the function of CA descrambling, and the CA card descrambles and then returns the received TS to a video decoding chip via a CA separation interface for video decoding, in order to eventually offer the video to users. This solution is the main form of Integrated Digital Televisions (IDTV). But in this solution, the TS transmitted in the CA separation interface is transparent and unprotected, in other words, the TS transmitted between the CA card and the video decoding chip is transparent and unprotected.
The other one is a CA board integration solution, which is mainly characterized in that a CA descrambling chip responsible for TS descrambling and a video decoding chip are arranged on the printed circuit board (PCB) of a user terminal, the CA descrambling chip performs CA descrambling on a received TS to obtain a transparent TS and sends the transparent TS to the video decoding chip for video decoding, in order to eventually offer the video to users. This solution is also the main form of Set-Top Boxes (STB) and Integrated Digital Televisions (IDTV). But in this solution, the TS transmitted between the CA descrambling chip and the video decoding chip is transparent and unprotected.
Typically, a TS transmitted between two devices can be copied if it is transparent, in this way, pirates are able to record programs corresponding to the TS by some technical means, and even to crack the TS scrambling key in real time by comparisons between transparent streams and encrypted streams. Therefore, it can be seen that the security of the TS transmission is severely influenced by the aforementioned two solutions.